The current firmware has problems measuring above 900MHz.
As example below a 1000 point scan of the "Open"
In my home build VNA I found that increasing the IF could help reducing noise.
As a test I increased the IF in the nanoVNA from 5kHz (as used in the first scan) to 12kHz.
As you can see in the second scan, using the same calibration data, the performance has increased.
There is more to test before I can release this.
Sadly this change does not help above 1.5GHz. Either the bridge has lost all directivity of the remaining SNR is too low to get a relevant signal
